The performance of a high-speed vessel is intimately linked to the orientation of the hull at speed. Planing hulls mostly rise and change trim angle in response to the hydrodynamic pressure field generated by the hydrodynamic flow. Conversely, the hydrodynamic pressure field acting on the wetted part of the hull is affected by the design of the hull form (See, e.g., U.S. Pat. Nos. 5,452,676; 5,456,202; 5,685,253; and 5,685,253). Generally, the major contributors to drag for a high-speed boat are due to the hydrodynamic pressure field (hydrodynamic pressure drag) and the hydrodynamic velocity boundary layer (hydrodynamic skin friction), in addition to the wave energy imparted.
A boat of length L traveling at a steady speed U at or near a free surface under gravity g tends to make large waves if and only if the Froude number F=U/√{square root over (gL)} takes values of the order of 0.55. At this particular value, the boat length is about half of the transverse wavelength 2πU2/g, and (roughly) equal and opposite waves from bow and stern add together. In this speed regime, wavemaking dominates all other physical processes. Most conventional marine vessels travel much slower (typically F<0.35) to avoid the energy-devouring wave generation phenomenon. In this slow regime, viscous effects dominate.
Although high-speed vessels must still have enough power to accelerate through the large-wavemaking regime (“hump speed”), at their higher design speeds (typically 0.7<F<1.3) less wavemaking is involved. While aerodynamic lift through the use of wings was applied to boats as early as 1910, (U.S. Pat. No. 978,311), Froude numbers did not exceed values on the order of 0.5. Even recent examples using aerodynamic lift to reduce drag such as ski boats (U.S. Pat. No. 4,284,027) would reach Froude numbers not exceeding values on the order of 1.5.
In prior art mono (v) type hulls, hydrodynamic-drag-reducing aerodynamic-lift has been generated solely at the expense of aerodynamic drag (U.S. Pat. Nos. 978,311; 1,015,568; 1,889,927; 3,648,640; 4,237,810; 4,284,027; 4,827,862; 5,111,766; and U.S. patent application no. 2005/0247251). In these examples, aerodynamic-lift devices at these lower velocities, if properly designed, reduced hydrodynamic pressure drag (due to a lower apparent hull weight) and lowered hydrodynamic friction drag (due to reduced wetted area) to some degree. The lower velocities kept the unavoidably induced aerodynamic drag somewhat in check in comparison with the hydrodynamic gains in drag reduction. Beside the fact that all prior art only pertains to Froude numbers less than values on the order of 1.5, the aerodynamic lifting forces in the prior art are estimated to constitute only a small fraction (10% or less) of the total weight of the vessel.
For multi-hull boats such as catamarans and tri-hulls operating at high velocities, the air compacted in the contracting tunnel or tunnels running along part or virtually the entire length of the hull produces upward lift (see, for example, U.S. Pat. Nos. 5,402,743; 5,458,078; and U.S. patent application no. 2005/0247251). This lift, as in many cases of high-power multi-hulls, determines the speed limitations of the craft. Beyond these limits, multi-hulls can lift off the water completely which results in dangerous loss of control. The amount of air captured by the inlet of the tunnel as well as the degree of air compaction has been entirely dependent upon the size of the tunnel, the degree of contraction, and the attitude of the boat during operation. The attitude (position and orientation of the boat with respect to the water's surface) of the boat is dependant upon many complex factors which, with the teachings of the present invention, can be controlled through the forward and aft lift-generating wings. For example, by using the forward wing or wings as the leading edge of the tunnel in accordance with one example embodiment of the present invention, not only can forward lift be controlled by adjusting the position and attitude of the wing but also can the amount of air captured by the tunnel be controlled. The synergy of controlling tunnel inlet conditions as well as forward lift achieved by the present invention gives additional control thus far unavailable in the prior art.
In other prior art (U.S. Pat. Nos. 4,926,778 and 4,940,433), forward and aft wings are used to control the pitch of boats. In U.S. Pat. No. 4,926,778, even with currently available high lift-to-drag ratio airfoils, the forward outwardly extending wings would be physically unable to generate sufficient lift to achieve the objectives of the present invention. The base angle of attack of seven degrees set forth in U.S. Pat. No. 4,926,778 is already very near the stalling angles for most airfoils. Hence, any condition such as “bow down” or “transom up” which would require additional lift through an increase of angle of attack actually would result in a lift drop off as a result of boundary-layer separation over the suction side of the airfoil.
In U.S. Pat. No. 4,940,433 and U.S. patent application no. 2005/0247251 a similar control scheme as in U.S. Pat. No. 4,926,778 is put forth albeit with a forward above deck airfoil. Just as in U.S. Pat. Nos. 978,311; 1,015,568; 1,889,927; 3,648,640; 4,237,810; 4,284,027; 4,827,862; and 5,111,766, attitude control is traded off for aerodynamic drag. In other words, the larger the attitude correction required the more aerodynamic drag has to be generated. Although from a safety perspective this may be desirable, from a performance perspective (speed as well as fuel efficiency) it is not. Additionally, the prior art discussed above only addresses the correction of pitch angles.
The terms “very-high-speed boat” and “VHS Boat” describes any surface vessel which is capable of traveling at speeds with Froude numbers ranging from around 4 to over values on the order of 10 and Reynolds Numbers (defined as Re=VL/ν) ranging from 107 to over 109, where V is velocity, L is length, ν is kinematic air viscosity. Under these conditions, wavemaking constitutes only a small fraction in the drag budget. VHS Boats may generate aerodynamic drag comparable to or even in excess of all other forms of drag which dominate for lower-speed vessels.
Fundamentally, lift cannot be generated without inducing drag. Hence, for a properly designed VHS boat (See for example U.S. Pat. Nos. 5,452,676 and 4,231,314) which already has substantially reduced wetted areas at very high speeds, any hydrodynamic drag reduction resulting from aerodynamic lift could be more than rendered entirely useless by the unavoidable induced drag of the lift-generating airfoils. In addition, the structures of the wing assemblies which support and allowed adjustment hereforeto considered essential to attaching wings to boats (U.S. Pat. Nos. 978,311; 1,015,568; 1,889,927; 4,284,027; 4,827,862; 4,926,778; 4,940,433; 5,111,766; and U.S. patent application no. 2005/0247251) add even more drag. Similar to lift, drag scales according to V2, where V is the vessel velocity. Therefore, it can be deduced that the drag of prior-art wing support and adjustment structures may increase by a factor of two to over four when transitioning from the above mentioned Re number and Fr number regimes the prior art is intended for to the very high speed (“VHS”) regime the current invention is intended for. These huge increases in drag with velocity render prior-art wing support and adjustment structures unfit for the VHS regime. Hence, the wing-support and adjustment structures in the present invention are not only aerodynamically concealed, but also prevent any increases in aerodynamic cross section through wings positioned away from or protruding substantially from the hull.
Additionally, the reduced hydrodynamic contact at high speeds can make a VHS boat dangerous to operate and very hard to control when pitch, roll, and yaw angles exceed certain boat, water, and ambient-dependent conditions. Negative pitch angles (“nose down”) may lead to the bow plowing into waves. This scenario, commonly known as “stuffing,” can lead to loss of control of the boat. Large positive pitch angles (“nose up”) may result in the entire boat lifting out of the water. Alternatively, under rough water conditions, the boat may leave the water for a substantial amount of time. If the craft leaves the water with a high nose-up attitude, re-entry in the water at the transom can cause the boat to violently rotate forward submerging the bow. This sequence leads to “stuffing” is extremely dangerous and most likely will lead to an accident through loss of control.
VHS boats generally operate in the planing regime where the sinkage is much smaller than the actual hull weight. With these “high riding” hulls, the longitudinal axis of inertia is close to or sometimes even higher than the waterline. These conditions may result in potentially dangerous instability called “chine walking” where the hull rolls (seen from behind) clockwise until the starboard chine will be sufficiently under water to generate a hydraulic pressure field with a moment about the longitudinal axis of inertia large enough to cause the hull to subsequently roll counterclockwise until the port chine will react similarly to induce again a clockwise roll. Under certain circumstances, the growth in angular amplitude of this instability may not be dampened resulting in dangerous uncontrollability of the boat.
A sufficiently large yaw angle may result in the equally dangerous phenomenon called “hooking” where the hull suddenly and uncontrollably spins as a result of sudden hydraulic drag generated from the bow (in waves or during porpoising) causing a sudden moment about the vertical axis of inertia.
Applicant has discovered that applying lift to the hull in a manner which decreases the hydrodynamic pressure drag also reduces the hydrodynamic friction drag as a result of decreased sinkage and wetted surface.
Applicant also has discovered that wings forward and aft of the center of inertia can generate a net moment which either lifts the transom, lifts the bow, or lifts transom and bow equally (“pitch neutral”).
Further, Applicant has discovered that wings in the vicinity of the center of inertia can generate an essentially “pitch neutral” lift force.
Applicant, in addition, has discovered that separate wings on the port and starboard side of the center of inertia can result in a net moment which either lifts the port side, lifts the starboard side, or lifts the port and starboard side equally.
Applicant, moreover, has discovered that vertical wings on the port and starboard side of the center of inertia can result in a net moment which pulls the boat towards the port side, pulls the boat to the starboard side, or keeps the alignment of the boat in the direction of travel.
Applicant has also discovered that the downwash, fundamental to the process of airfoils generating lift, can be effectively used to decrease aerodynamic pressure drag on the hull by increasing the base pressure levels at the transom surface.
In addition, Applicant has discovered that eroding the hull shape around the bow area of a mono (v) type hull, where static pressure contours reach the highest levels of the entire hull, result in reduced aerodynamic pressure drag.
Applicant has additionally discovered that a forward wing or wings designed as a leading edge to the tunnel or tunnels of a multi-hull vessel can be used to control lift generated in the tunnel or tunnels through controlling tunnel inlet conditions.
Applicant has also discovered that using wavy leading edges in the low-aspect wings used in this invention improves the lift to drag characteristics.
Applicant has further discovered that by providing aerodynamic air channels to feed the wings, the wings can be used effectively to generate lift without increasing the aerodynamic cross section of the vessel, while aerodynamically concealing the wing-support and adjustment structures.
Although each and every feature of the present invention can be individually practiced advantageously by those skilled in the art, applicant has discovered that selected combinations of the inventive aspects, or all of the inventive aspects, can be advantageously integrated in a synergistic manner.
It is an object of the present invention to increase the top-end speed of a VHS boat through the reduction of overall drag.
It is an additional objective of the present invention to provide methods and means to control trim by aerodynamically adjusting the pitching moment about the center of inertia.
It is yet an additional objective of the present invention to provide methods and means to support and control wings used to generate aerodynamic lift without drag-generating structures.
It is a further object of the present invention to provide methods and means to control the lift generated in a tunnel or tunnels of a multi-hull vessel by controlling the inlet conditions of the tunnel or tunnels.
It is still further an object of the present invention to provide methods and means for making a VHS boat more controllable and thus safer to drive at the performance envelope by reducing or controlling chine walking or heeling through an aerodynamically-generated rolling moment.
It is another object of the present invention to provide a method of making a VHS boat more controllable and thus safer to drive at the performance envelope by reducing or controlling hooking through an aerodynamically-generated yawing moment.
It is yet another object of the present invention to improve fuel efficiency through the reduction of overall drag.